Siemens S7-400 Installation Manual page 298

Glossary
Function
According to IEC 61131-3, a function is a ³ code block that contains no ³ static
data. A function allows parameters to be passed in the user program. Functions
are therefore suitable for programming complex functions, e.g. calculations, which
are repeated frequently.
Functional Grounding
Grounding whose only purpose is to ensure the intended function of the electrical
equipment concerned. Functional grounding short-circuits any noise that might
otherwise have a detrimental effect on the equipment.
Function Block (FB)
According to IEC 61131-3, a function block is a ³ code block that contains ³ static
data. An FB allows parameters to be passed in the user program. Function blocks
are therefore suitable for programming complex functions, e.g.
closed-loop controls, mode selections, which are repeated frequently.
Function Module (FM)
A programmable module which, in contrast to the CPU, has no multipoint interface
and can only be operated as a slave.
G
GD Circle
A GD circle comprises a number of CPUs which exchange data via global data
communication and are used as follows:
• A CPU sends a GD packet to the other CPUs.
• A CPU sends and receives a GD packet from another CPU.
A GD circle is identified by a GD circle number.
GD Element
A GD element is created through assigning the global data to be exchanged and is
clearly identified in the global data table by the GD identifier.
GD Packet
A GD packet can consist of one or more GD elements which are transmitted
together in a message frame.
Glossary-6
S7-400 and M7-400 Programmable Controllers Hardware and Installation
A5E00069481-04